Here's the updated code which should work. However wether I connect the Autonomer or not I always get -1. Even if I set a delay between clearing and reading I get the value almost immediately. It looks like as if the Z-Uno just ignores the delay(5000) completely.

Sounds like you have made some progress. I am not at home to try something with your code, maybe I can do this tomorrow.

It is hard to tell what tx-rx does to your particular device, but it is a very good question. When I test sensors, I limit data transmission to save (battery) power. This is one possible effect. I think a BME280 can self heat by about 0.5 degrees when polled at maximum speed versus once every second. So these are two real world examples of possible side effects.